The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
Usually, a person needing to wear spectacles and having thus a prescription filled by an ophthalmologist or an optometrist goes to the premise of an optician for choosing the spectacle frame of the future spectacles. The future wearer of the spectacles may try several spectacle frames and finally chooses one of the tried frames. The optician orders a pair of lenses corresponding to the prescription. The lenses sent to the optician are designed and manufactured according to optical criteria.
Depending on the service provided by the lens manufacturer, the optician may have to cut the lenses to fit the spectacle frame the person has chosen or in case of “remote edging” service the optician receives the lenses already cut and only has to fit them in the spectacle frame.
The inner circumference of the openings of the chosen spectacle frame (e.g. the openings of the frame where ophthalmic lenses are intended to be mounted) can be measured by a measuring device, for example a mechanical sensor. More particularly, the openings of the frame include the inner groove and the characteristics of the groove (tilt angle with the openings, depth of the groove, etc.) can be measured by the mechanical sensor in a measuring room.
The measurements performed by the mechanical sensor on the chosen spectacle frame make it possible to order ophthalmic lenses which fit the chosen spectacle frame, on the one hand, and the wearer prescription, on the other hand.
According to the measurements performed by the mechanical sensor in the measuring room, the optician or the provider of ophthalmic lenses are able to determine the edge and bevel the lenses to fit with the measurements performed on the chosen spectacle frame.
In the sense of the invention a step of cutting the lenses according to a spectacle frame shape is called “edging” and a step of forming a bevel on an external edged of the lens is called “beveling”.
The lenses provider has to ensure that the provided lenses are adapted to the wearer prescription and to the chosen spectacle frame.
For example, the lenses provider has to ensure that the future lenses can effectively fit the chosen frame which may have particular openings and groove.
Usually, the optical surfaces of the optical lenses are based on optical criteria, such as the wearer prescription, optical comfort and the measured parameter of the spectacle frame are used for the edging and beveling steps.
In some cases, the edging and beveling step can be proceeded according not only to the measured shape of the spectacle frame but also according to esthetic criteria chosen by the wearer. For example, the esthetic criteria may implies having front face edges of the ophthalmic lens substantially abutting with front faces of the chosen spectacle frame when the ophthalmic lenses are fitted in the frame. Another example is that in some cases, the wearer would like to have lenses with a more flat curvature than the curvature of the frame, so as to have a thinner global appearance of the eyeglasses, or on the contrary would like to have a stronger curvature than the curvature of the frame so as to have a more curved global appearance of the eyeglass.
According to the esthetic criteria of the wearer and his prescription it is not always possible to meet both optical and esthetic criteria.
Usually the lens manufacturer will select a determined front surface by selecting a semi finished lens according to optical criteria, and then the lens manufacturer will machine the final optical lens. The shape of the ophthalmic lens is then defined.
The person executing the edging and beveling steps, for example the optician, receives the ophthalmic lens and has to proceed to the edging and beveling steps according to the shape of the spectacle frame and to the esthetic criteria of the wearer.
Depending on the shape of the ophthalmic lens, it is not always possible to edge and bevel the ophthalmic lens according to the wearer criteria because of an improper lens shape (external shape of the lens, shapes of the front and rear surfaces of the lens, lens thickness, etc.).
For example, the bevel curve of the spectacle lens may be less steep compared with the curve of the frame, depending on the bevel position, and in this case the frame is deformed so as to be matched with the bevel curve.
Besides the fact that it is time-consuming, deforming the spectacle frame so to have the optical lens fit said spectacle frame, has several drawbacks.
First such deformation may modify the size of the frame beyond the values calculated when the bevel position was selected, and thus result in a deficiency of the outer diameter.
Additionally, such deformation may introduce additional mechanical stress on the optical lenses, which significantly increases the risk of fracturing the mineral coatings that may be present on the lenses.
Furthermore, such deformation may introduce mechanical stresses in the elements of the frame, particularly the mobile parts, such as the joint,
Such deformation of the spectacle frame may affect its appearance (destruction of symmetry change of the original curves of the model), more rudimentary means employed (pliers, heaters) can alter the aesthetics of the product (scratches, discoloration).
Such limitations are at least partly due to the fact that when determining the optical surfaces of the optical lens the shape, in particular the contour, of the spectacle frame is not considered.